App wont stay open

doom1992 · #1 02-Aug-2007, 12:49

can anyone tell me why my proggy will not stay open,

CPP / C++ / C Code:

#include <iostream>

int main () {
    
    int question5;
    
    std::cout <<"Would you like to erase your harddrive [Y/N]: ";
    std::cin >> question5;
    switch (question5) {
           case 'Y':
           case 'y':
                std::cout <<"Fool you have lost everthing";
                std::cout <<"----------------------------------------------------\n";
           
           break;
           
           case 'N':
           case 'n':
                std::cout <<"That was the wrong answer you fool";
                std::cout <<"----------------------------------------------------\n";
                
           break;
           
           default:
                   std::cout <<"You did not type a valid input you fool";
                   std::cout <<"----------------------------------------------------\n";
                   
           break;
           }
               
               
    std::cout <<"Press anything to exti";
    std::cin.get();
    
    return 0;
}

thanks

Kimmo · #2 02-Aug-2007, 14:23

You can't be serious! This is probably the third, at least the second, thread where you ask the EXACTLY same thing. Unless you start these out just for the fun of it, check out your previous threads for some answers.

doom1992 · #3 02-Aug-2007, 14:30

ive tried what you previously suggested and ive added it in this code and what your suggested is a load of old coblers, try and complie it.

Kimmo · #4 02-Aug-2007, 14:33

All I have been suggesting is to use

CPP / C++ / C Code:

while (cin.get() != '\n') {}

Now where in your code do I see that?

EDIT

I don't mean to be rude, but I haven't seen you actually getting back to threads you have started. There's no sign that you actually have taken heed of the advice given or tested out the stuff shown in the previous threads. The picture I'm slowly getting is that you start threads, maybe look at the responses, maybe test out the code and see it works, but then when you encounter basically exactly the same situation in another context, you don't want to go back to the old threads to look for advice. Instead you start a new one.

If there's something wrong with the advice people give here, tell them so! If it just doesn't work, tell so! Walking away without a word and starting new threads really doesn't help anyone, since you're basically getting the same responses to the same problems over and over again.

davekw7x · #5 02-Aug-2007, 16:00

Quote:

Originally Posted by doom1992

can anyone tell me why my proggy will not stay open,

There are actually two problems:

CPP / C++ / C Code:

    
    int question5;
    
    std::cout <<"Would you like to erase your harddrive [Y/N]: ";
    std::cin >> question5;

Now if the user entere y,or Y, or n, or N or anything else that can not be converted to a decimal integer, cin goes into a "fail" state. Nothing else can be done with cin until it gets reset. (I won't bother you with details.) So any further attempts to use cin will fail (like when you call cin.get()). That means it will return without waiting for any further input since it can't do anything.

However, when you fix that (by declaring char question5; instead of int question5; you still have the same action: It doesn't wait before closing.

Here is why:

When a C++ program gets something from stdin (with cin >> or with cin.get(), for example) here is what happens:

As the user presses keys, the characters are stored in a system buffer (somewhere outside your program's data space) until the user presses 'Enter'.

Nothing is available to any program functions until the user presses 'Enter'. After the user presses 'Enter', the characters are available to the program input functions.

All of the charactes are now in the system buffer and a newline character ('\n') is at the end.

Consider the following:

CPP / C++ / C Code:

    char question5;
    
    std::cout <<"Would you like to erase your harddrive [Y/N]: ";
    std::cin >> question5;

Suppose the user presses the 'y' key and 'Enter'. So the buffer contains two chars: 'y' and '\n'

Now cin >> question5 removes the character 'y' from the systembuffer and sets question5 equal to this value. The '\n' is still in the system buffer.

Later, you do cin.get() and it retrieves the '\n' that was left in the buffer, and the program exits.

A quick fix (but not necessarily the best thing to do from the point of view of future requiremenes) is just to put another cin.get():

CPP / C++ / C Code:

#include <iostream>

int main () {
    
    char question5;
    
    std::cout <<"Would you like to erase your harddrive [Y/N]: ";
    std::cin >> question5;
    switch (question5) {
           case 'Y':
           case 'y':
                std::cout <<"Fool you have lost everthing";
                std::cout <<"----------------------------------------------------\n";
           
           break;
           
           case 'N':
           case 'n':
                std::cout <<"That was the wrong answer you fool";
                std::cout <<"----------------------------------------------------\n";
                
           break;
           
           default:
                   std::cout <<"You did not type a valid input you fool";
                   std::cout <<"----------------------------------------------------\n";
                   
           break;
           }
               
               
    std::cout <<"Press 'Enter' to exit...";
    std::cin.get();
    std::cin.get();
    
    return 0;
}

Regards,

Dave

Footnote: After testing the above program, let me know if it doesn't work as it should. Then and only then, go back and change question5 to an int, as it was in your original program. You will find that it will not wait for any more input on cin, no matter how many cin.get() statements you add. When cin is in the "fail" state, it can't do anything.

doom1992 · #6 02-Aug-2007, 16:00

thanks for the advice kimmo

doom1992 · #7 02-Aug-2007, 16:06

thanks dave, the best answer ive got so far, but i added in

CPP / C++ / C Code:

std::cin.ignore(100, '\n')

under which is ment to clear the buffer, but sill have the same problem, is there anyother way to clear the buffer. Thanks

doom1992 · #8 02-Aug-2007, 16:08

dosent matter i added this under in the case y and case n blocks and it worked. Thanks for your help

davekw7x · #9 02-Aug-2007, 17:30

Quote:

Originally Posted by doom1992

added in

CPP / C++ / C Code:

std::cin.ignore(100, '\n')

I like that much better, since it removes not only the next char, but lots more (In case the user entered "yes" instead of "y" for example.) I was just trying to keep it simple with my "quick fix".

Note that cin.ignore() only works if cin is not in the "fail" state, so a more complete solution, in general, might be

CPP / C++ / C Code:

    std::cout <<"Press 'Enter' to exit...";
    if (!std::cin) {
        std::cin.clear(); // clear the "fail" flag
    }
    std::cin.ignore(100 , '\n'); // note that clear() does not empty the buffer
    std::cin.get();

The clear() would not be needed if you had only used cin for chars. It might be necessary if you had numeric input failures (trying to read an int but the user entered alphabetic chars, for example).

Quote:

Originally Posted by doom1992

but still have the same problem

Are you saying that the program that I posted did not work? It works for me as long as the user enters exactly one character before 'Enter'. Using cin.ignore(100,'\n') followed by cin.get() instead of two cin.get() calls should also work.

Regards,

Dave

Kimmo · #10 03-Aug-2007, 06:49

I began playing around and ran into the following problem.

I want to display lines of text a certain amount of lines at a time. After that certain amount of lines shown, I of course want the user to have time to read the text. The user presses Enter when he wants the next lines shown.

For example, if I use the following:

CPP / C++ / C Code:

cout << "Press Enter to continue. . ." << endl;
cin.get();

Now this works if the user just presses the Enter. But if the user writes "Hi" and Enter, the program runs three loops without stopping.

Now if I use something like this:

CPP / C++ / C Code:

while (cin.get() != '\n') {}
cout << "Press Enter to continue. . ." << endl;
cin.get();

This, on the other hand, doesn't work if the user just presses Enter. Here user is required to press Enter twice.

I tried to think but couldn't come up with a nice solution. I can't use cin.peek() because it waits for input too, if there is none. I thought maybe there is some way of determining if there is input pending for the program. But didn't find any (or just didn't understand. ios_base can be hard to get for us newbies).

So what's the simple solution I just fail to see here?

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